Electric circuit interrupter



Jan. 15, 1963 1 BAIRD ELECTRIC CIRCUIT INTERRUPTER Filed Oct. l, 1958 4Sheets-Sheet l 72 Inventor:

Lesl ie L.. Baird.,

is Attorneg.

Jan. 15, 1963 1 BAIRD l 3,073,936

ELECTRIC CIRCUIT INTERRUPTER Filed Oct. 1, 1958 4 sheets-sheet 2Inventar: Leslie L.. Baird,

b5 I H is Attorney.

Jan. l5, 1963 BAIRD ELECTRIC "CIRCUIT NTERRUPTER 4 Sheets-Sheet 5 Filed00T.. l, 1958 d P Wl. a O B t j. 8 n 8 9 e 2 H v e w M n .h l H I s n 0vA e s 9 2 w TF. L Mw 9 0 .M 22V i 0Q i .6 N o M u. 9 7 b i .I 7 no W, dd M His Attorn e5.

Jan. 15, 1963 I L. L. BAIRD 3,073,936

ELECTRIC CIRCUIT INTERRUPIER Filed Oct. l, 1958 l 4 Sheets-Sheet 4 iInventor:

Leslie L. Bai-rd,

is Attorney United States Patent hfice md 3,673536 ELEC'IREC CIRQIUI'IINTERRIJPTER Leslie L. Baird, warthmore, Pa., assigner to GeneralElectric Company, a corporation of New York Filed (bet. l, 1958, Ser.No. 764,642 33 Claims. Si Zitti-168) This invention relates to electriccircuit interrupters or breakers, and more particularly it relates toimprovements in the contact structure and in the mounting ibase of a lowvoltage air circuit breaker.

One object of the invention is the provision of a relatively simple,lightweight and compact circuit interrupter contact structure havingabutting movable and relatively stationary contact members so orientedwith respect to each other that a plurality of stationary contactelements can conveniently be associated with each movable contactmember.

It is another object of the invention to provide in an electric circuitinterrupter the combination of an arc chute of the type includingarc-chopping metal plates and improved contact structure including aplurality of cooperating contact surfaces arranged to provide at leasttwo parallel paths for current flow, all of the contact surfaces beingdisposed within the arc chute for substantially simultaneous separationduring a circuit interrupting operation.

Another object of this invention is the provision, in a circuitinterrupter contact structure, `of a pivotally mounted, substantiallytorsion-free contact arm connected to an actuating member and having anaxially offset contact surface disposed for movement into and out ofcircuit making engagement with a cooperative contact surface of arelatively stationary contact member.

Still another object is the provision, in a contact structure includinga relatively stationary bracket having a removable pivot pin forpivotally supporting a movable contact arm, of inexpensive and expedientreleasable clamping means associated with the pivot pin intermediate itsends for preventing removal thereof.

A further ofbject of the invention is to provide a circuit y'breakermounting base comprising a sheet of substantially uniformly thickinsulating material supporting the breaker studs and formed in a mannerto provide unusually great strength and rigidity in the areas betweenadjacent breaker studs.

It is a general object of the invention to provide an improved circuitbreaker of the character `described hereinafter.

In carrying out my invention in one form, an electric circuit breaker ismounted on a b-ase member comprising a sheet of electric insulatingmaterial of substantially uniform thickness. For improved rigidity, theinsulating sheet is molded in the form of channel-shaped sections in theareas where the current-conducting studs of the breaker are supported bythe base. Mounted on the base is a relatively stationary contactcomprising: an electroconductive member electrically joined to one ofthe breaker studs, at least one contact finger pivotally supported 'bythe electroconductive member, and spring means for biasing the contactfinger and permitting deflection thereof. A bracket is mounted on thebate in spaced relation to the stationary contact, Iand a movablecontact member is pivotally connected to the bracket for rotation aboutan axis oriented approximately perpendicular to the pivotal axis of therelatively stationary contact finger. The movable contact member iselectrically connected to another breaker stud, and it has a transversecontact surface disposed for circuit making engagement with aco-operative abutting contact surface of the finger. An actuating memberis connected to the movable contact member for angularly moving thelatter member and its contact surface into abutting engagement with thecooperative contact surface of the finger, thereby deflecting saidfinger.

In one aspect of the invention, the bracket includes 'a pair ofupstanding lugs supporting a removable pivot pin to which the movablecontact member is pivotally connected. Axial movement and hence removalof the pivot pin is prevented by means of a releasable clamp connectedto the pin intermediate the upstanding lugs. The. releasable clampcomprises a resilient coil encircling and firmly grasping the pin, theends of the coil being arranged for cooperative movement to expand thecoil circumference and thereby rel-ease the pivotpin.

In another aspect of the invention, the movable contact member comprisesan elongated arm, and the portion of the arm that carries the contactsurface is axially oSCt: with respect to the pivotal connection betweenarm and bracket. This movable contact arm is constructed and arranged sothat the lines or action of the resultant forces acting on the arm atits pivotal connection, at its connection to the actuating member, andat the contact surface. when in circuit-making engagement with thecooperative contact surface of the relatively stationary contact fingerall lie in a common plane, whereby substantially no twisting moment isestablished in the contact arm.

In still another aspect of the invention, the axially olfset end of the.movable contact arm and the portion of the relatively stationary contactfinger that carries the c0- operative contact surface are disposed in anarcing chamf ber of an arc chute. The arc chute encloses the electricarc ydrawn between the respective Contact surfaces when separated duringa circuit 'breaking operation, and the arc 4is extinguished in the chutewith the aid of a plurality of spaced-apart, arc-chopping metal plates.To increase the current rating of the breaker, a second contact fingeris conveniently disposed adjacent the first-mentioned finger, and thesecond finger is provided with a contact surface disposed in the arcingchamber for abutting engagement with the contact surface of the movablearm. Thus two parallel points of circuit-making engagement are providedbetween the movable and relatively stationary contacts.

My invention will lbe better understood and its various objects andadvantages will be more fully appreciated from the following descriptiontaken in conjunction with the accompanying drawings in which:

FIG. 1 is a side elevation of a circuit breaker contact structure andmounting base embodying a preferred form of my invention, with the basemember in section and the movable contact member of the contactstructure shown in its closed circuit position;

FIG. 2 is an enlarged front elevation of the contact Structureillustrated'in FIG. 1, with the movable contact member moved to its opencircuit poition;

FIG. 3 is a plan sectional view of the contact structure of FIG. 2 takenalong the line 3 3 and showing the Stationary contact mem-ber with thecooperating movable Contact member in an intermediate position;

FIG. 4 is a prole view of one arm of the movable contact member shown inFIGS. 1 and 2;

FIG. 5 is a plan view, partly in section, of an alternative embodimentof the stationary contact member;

FIG, 6 is a sectional view of the FIG. 5 embodiment along the line 6 6;

FIG. 7 is an enlarged side elevation, partly in section, of the arcchute shown in block form in FIG. 1;

FIG. 8 is a front elevation of a preferred embodiment of the base memberillustrated in section in FIG. 1, two breaker studs being shown securedto the base member by representative supporting angles; and

FIG. 9 is an enlarged sectional view of the base member of FIG. 8 alonglines 9 9. v

Referring now to FIG. 1, I have shown an electric circuit breaker orinterrupter comprising a base member 11,

a relatively stationary contact member 12 mounted on the base, anelectroconductive bracket 13 mounted on the base in spaced relation tothe stationary contact member, a movable contact member 14 pivotallysupported by bracket 13 and disposed in cooperative relationship withthe stationary contact member 12, and actuating means such as a crossbar15 coupled to the movable contact member 14 for moving this member intoand out of circuit-making engagement with the stationary contact member12. The components 12, 13 and 14 comprise the contact structure of onepole unit of an alternating or direct current circuit breaker orinterrupter. Although I do not wish to be limited thereto, the preferredembodiment of contact structure has been particularly designed for a3pole A.C. circuit breaker, and for this purpose two other pole units(not shown) substantially identical to that shown in FIGS. l and 2 wouldbe mounted for gang operation on the base member 11.

In the preferred embodiment, the stationary contact member 12 of theillustrated pole unit is connected to one phase of a 3phase A.C.electric power source or bus by means of an upper current-conductingstud 16; and by means of the bracket 13, an operating coil 17 of anovercurrent trip device 18 and a lower current-conducting stud 19, themovable contact member 14 is connected to a corresponding phase of aload circuit (not shown). The other two companion pole units of a 3-polebreaker are connected by corresponding means tothe respective phases ofthe 3phase A.C. bus and load circuit. The electric power bus, not shownin the drawings, may be part of a 600-volt system that is capable ofproducing as much as 25,000 amperes short-circuit current at 600 volts,and the contact structure of the circuit breaker, which is designed tocarry 600 amperes continuously without exceeding permissible limits oftemperature rise, can successfully interrupt this maximum short-circuitcurrent. Of course the circuit breaker may be applied in any electricpower system to which its capabilities are suited, and theabovementioned ratings have been set forth only for the purpose ofillustrating one range of magnitudes specifically contemplated.

The base member 11 supports all of the current-conducting studs of thebreaker and the other breaker parts connected directly to the studs. Asillustrated in FIG. l, the base member 11 in one embodiment of myinvention comprises a single sheet 20 of electric insulating material ofsubstantially uniform thickness. The sheet 20 is shaped to form twoseparate channel-shaped sections or depressions at 21 and 22, and thebottoms of these sections are provided with apertures for snuglyadmitting and partially supporting the breaker studs 16 and 19,respectively. For the purposes of the present description, the contactstructure 12-14 will be considered mounted on the front of the base 11,and the bus and load circuits to which the breaker studs arerespectively connected are located behind or to the rear of the base (inother words, .on the opposite side of the base member from the circuitbreaker). In order to provide extra sturdiness and rigidity, the basemember 11 may include a metal frame 23 disposed behind the insulatingsheet 20 for supporting the sheet adjacent its outer edges. The basemember will be described hereinafter in greater detail in connectionwith FIGS. 8 and 9.

The stationary contact member 12 is mounted on a portion of upperbreaker stud 16 emerging from within the channel shaped base membersection 21. As can be seen in FIG. l, the emergent portion of the stud16 is secured to the sheet 20 of base member 11 by suitable supportmeans such as generally L-shaped angles 24 and 25. The angles 24 and 25are respectively disposed above and below stud 16 and are fastenedthereto by three copper rivets or the like. The lower angle 25 isprovided with a pair of tapped holes, and a pair of appropriate bolts 27is used to secure this angle to the base member 11 below the lower lipof its depressed section 21. As can be seen in FIG. l, an integral part28 of the supporting angle 25 is disposed adjacent the front surface ofthe sheet of insulating material 20 intermediate the channel-shapedsections 21 and 22. The supporting angle 24, which extends above thebreaker stud 16 as is shown in FIG. l, serves as an are runner incooperation with the stationary contact member 12. This angle isprovided with a stud 29 for securing it to the insulating sheet 20adjacent to the upper lip of the depression 21 formed therein.

The end of breaker stud 16 extending forward from the base member isdivided into two horizontally diverging branches, whereby this emergentportion of the stud in plan view has a generally Y-shaped appearance. Inthe preferred embodiment of my invention illustrated in FIGS. 1, 2 and3, the stationary contact member 12 comprises a plurality of elongatedcontact elements or fingers 30 each pivotally supported intermediate itsends on the outer end of one of the diverging branches of the breakerstud 16. For this purpose, the outer end of each diverging branch isprovided with a generally cylindrical bearing surface 31, the axis ofthis surface being oriented in a vertical direction as seen in side andfront views, FIGS. 1 and 2. The length of the bearing surface 31 can bemade sufficient to accommodate two contact fingers 30 in side-by-siderelation, and the surface 31 is recessed so that a shoulder is formed ateach of its ends to prevent movement of the adjacent contact fingers ina vertical or axial direction with respect to the bearing surface.

Each of the two bearing surfaces 31 of the breaker stud 16 provides afulcrum for a set of two parallel contact fingers 30, and the pivotalconnection between each contact finger and the breaker stud forms acurrent-conducting joint. As can be clearly seen in FIGS. 2 and 3, thecontact fingers 30 are arranged in adjacent pairs. The fingers of eachpair are respectively supported on opposite bearing surfaces in opposingrelationship with respect to each other, the opposing fingers of eachpair being pivotally movable in a common horizontal plane. The opposingor inner ends of the contact fingers of each pair move in separate,relatively short arcuate paths which are respectively parallel to thearcuate paths of movement of the corresponding ends of the adjacent pairof fingers. The opposing ends of the fingers 30 are respectivelyprovided with generally fiat, complementary contact surfaces 32 normallydisposed in a common vertical plane as viewed in FIGS. l and 2.

The inner end of each contact finger 30 is also provided with anextension 33 disposed to engage a common stop 34 for determining thelimit of the arcuate movement of the contact surface 32 in onedirection. The stop 34, as has been shown in FIGS. 2 and 3, comprises apin vertically disposed intermediate the divergent branches of thebreaker stud 16 and flxedly connected to the upper and lower supportingangles 24 and 25.

Associated with the outer end 35 of each contact finger 30 is suitablespring means, for example, the illustrated tension spring 36 which maybe anchored at one end to a fixed member such as provided by thelaterally extending lugs 37 of the supporting angles 24 and 25. Thus,spring means 36 establishes a biasing torque in the contact linger 30tending to move the contact surface 32 along an arcuate path in aforward direction away from the base member 11, and as is clearly shownin FIG. 3, such movement by the finger is limited by stop pin 34. As aresult of this arrangement, relatively limited deflection of eachcontact finger in a rearward direction is permitted.

The biasing torque is opposed and overcome and each contact finger 30 ofthe relatively stationary contact member 12 is tilted slightly on itsfulcrum 31 by the aetion of the movable contact member 14. As will befully explained hereinafter, the movable contact member 14 includes apair of arms respectively provided with contact surfaces 67 which movein parallel planes disposed approximately perpendicular to the planesdefined by the parallel arcuate paths of the contact surfaces 32 of eachset of adjacent fingers 3d. The actuating means 15 provides actuatingforce 'for moving each contact surface 67 of member 14 into and out ofcircuit-making abutting engagement with adjacent contact surfaces 32 oftwo parallel contact lingers. During a circuit making operation, the`contact surfaces 67 are jointly carried rearwardly `from their open'circuit position into substantially simultaneous engagement with all ofthe cooperating contact surfaces 32. FIG. 3 shows the relative positionsof the parts when circuit-making engagement is initially established,'and further rearward movement of the contact surfaces 67 to their`fully closed position Iforces spring means 36 to stretch `as theyieldably supported contact fingers 3d til-t on fulcrurms 31. ln thismanner conventional contact wiping action is obtained.

As is most clearly seen in FIG. 3, the relatively stationary contactmember 12 is arranged so that the arcuate path of the portion of eachcontact surface 32 engaged by a contact surface 67 of the movablecontact member is spaced from the 'fulcrum 31 a distance greater thanthe length of the moment arm of the line of action of the tension spring36 with respect to fulcrum 31. In other Words, the line of action of thebiasing spring force is placed relatively close to the fulcrum, and theforce exerted by the contact finger 3i) on fulcrum 31 will be more thantwice the amount of force applied to contact surface 32 by the movablecontact member 14. This results in sufficient 'force at the fulcrum toensure a good current-conducting joint between lingers 30 and breakerstud 16.

The details of the above-described relatively stationary contact member12 -have been more fully disclosed and are claimed in Patent3,033,964-Titus, issued on May 8, 1962. An alternative embodiment ofthis member is shown herein in FIGS. and 6. Here the opposing contactfingers 30a are yieldably supported on breaker stud 16a by meansincluding two pivot pins 40. Each pivot pin 40 extends betweenspaced-apart walls 41 and 42 of each diverging branch of the ybreakerstud 16a, and two adjacent contact fingers 30a are disposed on eachpivot pin between walls 41 and 42. Suitable spacing means such as awasher 43 may be located between the contact fingers 30a. Biasing torqueis established in each pair of contact lingers 36a by means of a helicalcompression spring 36a disposed in a well 44 located in the breaker stud16a. The compression spring 36a acts against a disk-like insulatingmember 4S which supports and guides a force transmitting link 46. Thelink 46 is recessed at one end for receiving the midportion of anequalizer pin 47, `and the respective ends of pin 47 extend on oppositesides of link 46 into cooperating holes 4% located in the contactfingers 30a. It should be apparent from inspection of FIG. 6 that thisstructure ensures that substantially equal biasing torque is establishedin the adjacent contact fingers 30a by the single compression spring36a. The insulating member 45 is used to prevent current conduction bythe spring 36a. Pivotal movement of each contact finger 36a under theiniuence of the biasing torque is limited by an extension 49 of thefinger which is ydisposed to engage an inclined stop surface 50 of thebreaker stud 16a.

Returning now to FIGS. y1 and 2, it can be seen that theelectroconductive bracket 13 for supporting the movable contact member14 is mounted on base member 11 by means of a pair of suitable bolts 51or the like. An integral part 52 of the bracket 13 is disposed adjacentthe front surface of the insulating sheet 20 0f base member 11intermediate the channel-shaped sections 21 and 22. A rigid reinforcingmember 53 is disposed adjacent the opposite surface of the sheet 20intermediate the channel-shaped sections 21 and 22 in overlappingrelationship with the integral parts 28 and 52 of the supporting angle25 and the bracket 13, respectively. The reinforcing member 53 may bepart of the metal frame 23, and it is provided so that the loading ofthe insulating d sheet 211 in this area will be in compression ratherthan in iiexure. 1n other words, the reinforcing member 53 provides abacking for the sheet 2t? in an area that would otherwise be stressed inflexure whenever the circuit breaker is closed due to the yforce ofactuating means 15 applied to the movable contact member 14 and hence tothe supporting bracket 13 and to the cooperating station-- ary contactmember 12 and its supporting angle 25. A channel 54 of insulatingmaterial is disposed intermediate the reinforcing member 53 and the rearof sheet 20 to provide additional electrical insulation between thesides of member 53 Tand the fastening bolts Z7 and 51.

The bracket 13 includes a pair of spaced-apart upstanding lugs 55 and 56projecting in front of base member 11. A removable pivot pin 57 issupported by the lugs 5S and 55, the axis of the pivot pin extending ina horizontal direction lgenerally parallel to the plane of the basemember 11 as viewed in FIGS. l and 2. The pivot pin 57, which projectsbeyond the outwardly facing side of each lug, is retained in place by areleasable clamp 58 connected to the pin intermediate lugs 55' and 56.The clamp 58 comprises a resilient helical coil loosely encircling pin57, the length of the helix corresponding approximately to the spanbetween the lugs. The opposite ends of the coil of clamp 58 extendtangentially therefrom and are arranged for movement between first andsecond cooperating position-s. In FIG. 2 the ends are shown in .aposition wherein they releasably en-gage each other, and in thisself-locked position the circumference of the coil is contracted forrmly grasping the encircled pin and preventing axial movement andremoval thereof. By separating the ends and permitting them to assumetheir other position in accordance with the resilience of the coil, thecircumference of the coil can be enpediently expanded for assembling ordisassembling purposes. It will, of course, be understood that thisarrangement of `the releasable clamp S8 could be reversed, that is, theresilient coil could be designed normally to grasp the pivot pin 57, thecoil circumference being expanded to release the pin by forcing the coilend-s away from eachother.

The outwardly facing side of each opstanding lug 55, 56 is provided witha substantially lia-t slide surface 59. Disposed adjacent the slidesurface 59 of lug 55 and rotatably mounted on pivot pin 57 is one end 60of an elongated contact arm o1; and disposed adjacent the slide surface59 of lug 56 and rotatably mounted on the pivot pin 57 is one end 62 ofan elongated contact arm 63. The conta-ct arms d1 and 63 are arranged ingenerally parallel relation for joint operation and comprise the movablecontact member 14.

The connection between each movable Contact arm 61, 63 and theelectroconductive bracket 13 is arranged to provide three separatecurrent-conducting joints. The iirst such joint is provided by thebearing surfaces between the contact arm and the pivot pin S7 on whichit rotates, that is, between pin 57 and the periphery of a hole whichhas been located in the one end et?, to accommodate the pin 5'7. Thesurface of the pivot pin 57 and the periphery of hole 65 may be silverplated and burnished to ensure a wear-resistant, low electric resistancecurrent-conducting path.

The pivoted end nti, 62 of each movable Contact arm 61, 63 has apertaining slide surface 6a on its relatively broad inner side, i.e., onthe side of the contact arm facing the companion contact arm. The slidesurface ed is disposed generally parallel to the adjoining slide surface59 of the lugs 55, 56 of the supporting bracket 13. Both slide surfacesS9 and 64 are disposed substantiatly perpendicular to the axis of pivotpin 57 which corresponds to the axis of rotation of the movable contactarms 61 and d3. In accordance with the teachings of Patent2,962,573-Scul1y, issuedv on November 29, 1960', the slide surface 64includes a raised section which, as can best be seen in the FiG. 4profile View of Contact arm 61, preferably comprises a portion of acylinder. The crest of this raised section is oriented so that itextends in a direction substantially perpendicular to the longitudinalcenterline of the contact arm, and it is intersected by the hole 65provided for pivot pin 57. The crest of the raised section of slidesurface 64 is contiguous with slide surface 59 of bracket 13, andpivotal movement of the Contact arm or pin 57 causes the crest to slideover the surface S9. The contiguous portions of the slide surfaces 59and 64 define a line Contact which provides the secondcurrent-conducting joint between each movable Contact arm and thesupporting bracket. Of course, as an alternative to the specificarrangement illustrated in FIGS. 2 and 4 and described above, a raisedsection could be located on slide surface 59 and the slide surface 6dcould be made substantially llat.

Contact pressure at the joint formed by the contiguous slide surfaces ismaintained by means of an electroconductive spring member 66 whichpreferably comprises a U-shaped spring clip, the upstanding legs of theclip 66 being split for respectively bearing against the relativelybroad outer sides of each contact arm 61, 63 at points disposed onopposite sides of the pivot pin 57. See FIGS. l and 2. Theelectroconductive spring member 66 is secured to the bracket 13, andsince it also is in engagement with each movable contact arm it providesthe third current-conducting joint. ln addition, spring member 66supplies a force which maintains contact pressure between the contiguousslide surfaces 59 and 64. This force is supplemented by anelectromagnetic force whenever the movable Contact member 14 isconducting current. Whenever the parallel Contact arms 61 and 63 conductalternating current, a magnetic force is established tending to reducethe spacing between these two arms and thereby establishing additionalcontact pressure at the contiguous slide surfaces 59 and 64, themagnitude of this force being proportional to the square of the currentmagnitude.

The diameter of hole 65 in the movable contact arms is made slightlygreater than the diameter of pivot pin S7. This arrangement permits thecontact arms 6l and 63 to rock on pivot pin 57. The crest of the raisedsection of slide surface 64 provides a fulcrum for the rocking movementof the arms. This arrangement allows for a certain degree ofmisalignment of the various parts and a liberal manufacturing toleranceWithout .adversely affecting the positiveness of the electric contactbetween the movable members and the supporting bracket. y utilizingthree parallel current-conducting joints for each of the two parallelarms, the overall electric resistance of the pivotal connection islowered thereby decreasing temperature rise. ln this manner it ispossible to obtain a successful Contact structure without theconventional flexible braids or conductors.

The corresponding free ends of the contact arms 61 and 63 are providedrespectively with elongated, transverse contact surfaces 67 disposed forabutting engagement with the contact surfaces 32 of the relativelystationary contact fingers 3?. Each contact surface 67 preferably isgenerally cylindrically shaped and defines with the abutting surface 32of each cooperating nger 30 a relatively narrow area of contactengagement. The length of this thin area of engagement or line contactbetween each movable contact arm and cooperating linger is less than thelength of the contact surface 67, as is apparent in FiGS. l and 2, andthe curved contact surface 67 extends beyond the generally flat contactsurface 32 at both ends of the line contact.

Rotary movement of the contact arms 61 and 63 on pivot pin 57 carriesboth contact surfaces 67 through arcuate paths which define verticalplanes intersecting at approximately right angles the parallel planesdclined by the arcuate paths of the relatively stationary contactsurfaces 32, as viewed in FlGS. 1-3. In other words, each movablecontact arm is disposed to move in a plane generally perpendicular tothe longitudinal centerline of a stationary contact linger-the axis ofrotation of the movable arm being oriented parallel to the plane ofmovement of the relatively stationary contact finger and the axis ofrotation of the relatively stationary contact finger being orientedparallel to the plane of movement of the movable contact arm. Thisarrangement permits the convenient utilization of two separatestationary contact fingers for each movable contact arm, whereby fourseparate points of circuit-closing engagement are provided between themovable contact member 14 and the relatively stationary contact member12.

By utilizing the structure and orientation of the movable and relativelystationary contact members described above, l am able to realize anumber of important advantages and improvements over prior art circuitbreakers. The desirability of a multi-point contact arrangement is, ofcourse, recognized by those skilled in the art. Since the electricresistance of any single-point contact cannot practically be reducedbelow a finite minimum value regardless of the contact force applied,total contact resistance is most efficiently reduced by providingparallel points of engagement between the cooperating contact surfaces,substantially the same amount of contact force being applied at eachpoint. In this manner thc temperature rise of the contact structure isdecreased so that significant economies can be realized in the requiredminimum sizes of the various current-carrying parts. Two parallel pointsof contact will enable the breaker successfully to carry at least 22Samperes continuously while four parallel points of contact enable thebreaker successfully to carry 600 amperes continuously at 600 volts A.C.By means of the specific orientation of the movable and relativelystationary contact members 14 and 12 of the present invention, I obtainthe four points of contact between the abutting contact surfaces 67 and32 with only two movable contact arms having only one transverse contactsurface each. This relatively simple and compact arrangement permits areduction in the mass of the moving parts thus permitting higheroperating speeds while lessening impact stresses and thereby prolongingthe mechanical life of the contact structure.

The cooperating contact surfaces 32 and 67 preferably are made of silvertungsten carbide material which will successfully perform not only thecontinuous currentcarrying function of the contacts lbut also therequired circuit making and breaking duty without appreciable contacterosion or pitting or contact welding as a result of electric arcing.Therefore it is not necessary to provide separate arcing and maincontacts, and as a result the complexity of the contact structure aswell as the necessity for and problems of maintenance are minimized. Dueto the particular orientation of the respective elements of thecooperating Contact members 12 and 14, all contact surfaces 32 and 67can be conveniently located in a common arcing chamber of a single arcchute for the purpose of interrupting the electric arc drawn betweenthese cooperating contact surfaces during a circuit opening operationthereof. This latter point will be discussed in greater detailhereinafter.

In order to obtain a compact arrangement at the cooperating contactsurfaces 32 and 67, the contact arms 61 and 63 are spaced closertogether at their corresponding free ends than at the pivot pin 57. Asis shown in FIG. 2, this has been accomplished by axially offsetting thefree ends of the contact arms with respect to the pivotally connectedends 60 and 62, respectively. In other words, each free end is disposedinside a plane normal to the pivot pin 57 that intersects the bearingarea providing the pivotal connection between the associated movablecontact arm (the periphery of hole 65) and pin 57. Thus, the center ofthe circuit-making surface area of the contact surface 67, that is, thecenter of the area of surface 67 which engages the contact surfaces 32of the stationary contact fingers 30, defines with the center of thepivotal connection to pivot pin 57 a straight line 68 which intersectsthe axis of rotation (the axis of pivot pin 57) 'at an oblique angle.See HG. 4.

`In accordance with my invention, the contact arms are oppositely offsetat intermeidate portions 69. As indicated in FIG. 4 the offset portion69 of each arm is provided with a transverse hole 76 the centerline ofwhich is oriented parallel to the pivot pin 57. An actuating member suchas a cylindrical impelling shaft 71 is rotatably disposed in hole 7i),and by this means actuating force is applied to the movable contactmember 14 lfor jointly moving the contact arms 61 and 63 between openand closed circuit positions. The offset portion 69 of each of thecontact arms is so arranged that the line of action of the resultantactuating for-ce intersects the straight line 68. In other words, acommon plane of action and reaction is defined by the center of thebearing surface between the impelling shaft 71 and the offset portion 69of the contact arm, the center of the pivotal connection between pivotpin 57 and the pivoted end of the arm, and the center of the engagingarea of contact surface 67. This plane will include the intersection ofthe respective planes of movement of the cooperating movable andrelatively stationary contact surfaces 67 and 32. As a result, there isnot net component of actuating force having a moment arm with respect tothe straight line 63, and there is substantially no torsion or twistingtendency in the contact arm in its closed circuit position. Such atendency would be undersirable because it would cause uneven forces-along the length of the crest of the raised section of slide surface`64 with respect to the continguous slide surface S9, whereby theeectiveness of this current-conducting joint between the movable contactmember 14 and the supporting b-racket 13 would be seriously impaired. Bysubstantially eliminating torsion in each of the contact arms 61 and 63,the current-conducting integrity of the area contact joint formedbetween the pivot pin 57 and the proximate end of each arm is alsopreserved.

In the vicinity of the offset portions 69 of the contact arms 61 and 63,protrusions 72 are formed. These protrusions 72, which preferably are inthe yform of curved embossments on the inner sides of the contact arms,are respectively disposed to extend in overh'anging relationship withthe lugs 55 and 56 of bracket '13. In this manner, thecurrent-conducting joints formed by the contiguous slide surfaces 59 and64 are shielded from the electric arc and arc products which may beproduced during circuit breaking action of the Contact structure. Theprotrusions 72. will prevent particles of foreign matter produced duringcircuit breaking action from entering these joints by straight-linepaths from the area of arc interruption. Such foreign matter, ifpermitted to enter a joint, could cause excessive wear and increasedcontact resistance. The shielding arrangement just described is thesubject matter of Patent 3,023,292- Stewart issued on February 27, 1962.

The impelling shaft 71 fits relatively loosely in the holes 70 in theoffset portions 69 of the movable contact arms 61 and `63, whereby eacharm can slide on shaft 71 while rocking on pivot pin 57. Thus thecontact surface 67 of each :arm is free to move in a lateral ortransverse direction, and such lateral movement is controlled byresilient means associated with the contact arm. As is shown in FIG. 2,the resilient means preferably -comprises a helical spring 73 disposedon impelling shaft 71 intermediate the contact arms 61 and 63. Thespring 73 applies a transverse force to each contact arm and establishesin the arm a relatively weak biasing torque with respect to the pivotprovided by the line contact at the joint formed formed by thecontiguous slide surfaces 59 land 64. This ybiasing torque is in adirection tending to spread apart the contact arms. Such movement ofeach contact arm is stopped and its normal position is determined by abushing 74 disposed on shaft l@ 71 between a retaining ring 75 or thelike and the circular outer side of the offset portion 69 of the arm.

During circuit making `action of the contact structure, contact surface67 comes into abutting engagement with contact surface 32 of arelatively stationary contact finger 30, and as the cooperating contactsurfaces wipe the contact finger 30 is tilted on fulcrum 31 inopposition to its biasing torque. The arrangement is such that atransverse force is supplied to contact surface 67 by contact surface 32as the contact linger 30 moves pivotally on fulcrum 31. Due to theresilient means 73, the movable contact arm yields to this transverseforce and the contact surface 67 is able to move laterally whilefollowing the `arcuate path of Contact surface 32. As a result, therelative movement between the cooperating contact surfaces 32 and 67 isreduced thereby reducing the amount of friction between thesecooperating surfaces and improving the performance of the contactstructure. Such an arrangement is in accordance with the teachings ofPatent 2,938,986, Baskerville et al. issued on May 3l, 1960.

The movable contact member 14 is coupled to the actuating means orcrossbar 15 by means of the impelling shaft 71 and an actuating member76 preferably comprising a generally U-shaped connecting link securelyfastened to the crossbar. Each leg of the connecting link 76 is providedwith an extension which, as is clearly seen in FIG. l, is connected tothe pivot pin 57. Thus, the crossbar 1S is supported for pivotalmovement on pin 57. The end portions 77 of impelling shaft 71 extendlaterally from the contact arms 6.1 and 63 and are made eccentric withrespect to the cylindrical body of this shaft. The end portions -77 arecoupled to the connecting link 76 in a manner permitting controlledrotation of the shaft 71. This has been done by providing each endportion 77 with flat sides forming a hexagon, parallel sides of thehexagon being positively but resiliently locked between a shoulder ofthe connecting link 76 and a cooperating cantilever flat spring 7 Scarried by link 76. See FIG. 1.

By means of a conventional open-end wrench applied to the hexagonal endportion 77, the shaft 71 may be rotated to any one of six angularpositions. In each of these six positions, the movable contact member 14is located in a different relative angular position with respect to thecrossbar 15 and with respect to the relatively stationary contact member12. The purpose of this adjustment is to accurately establish the fullyclosed position of the movable contact member regardless of liberalmanufacturing tolerances, whereby the desired amount of contact wipe canbe precisely obtained. The illustrated contact wipe adjusting means hasbeen more fully disclosed and is claimed in Patent 2,938,095-Baskerville issued on May 24,

The crossbar 1S is connected to a circuit breaker operating mechanism bymeans of another link 7 9 and a connecting member 89. The operatingmechanism, which has not been shown, may be of any suitable type formoving the connecting member 80' in a generally horizontal direction (asviewed in FIGS. l and 2) and thereby reciprocally carrying the crossbar15 about its pivot between first and second relatively fixed positions.

The crossbar 15 may be extended across the width of the circuit breakerfor connection in a similar manner to other pole units of a multipolecircuit breaker. An

f isolating barrier S1 of insulating material is shown mounted on thecrossbar 15 in FIG. 2. Other barriers 82 are provided for the purpose ofisolating the various currentconducting parts of the illustrated poleunit from the corresponding parts of adjacent pole units and fromground. A suitable arc chute 83, shown in block form in FIG. l, is usedfor the conventional purpose of arc extinction. At a point above the arcchute 83, as viewed in FIG. l, a ridge 84 is formed in the insulatingsheet 20 of the base member 11. The ridge 84 shields the upper edge ofthe metal frame 23 from the direct blast of ionized arc gases duringcircuit interruption, thereby preventing ground currents in this area.

An arc chute 83 particularly well suited for use in cornbination withthe above-described contact structure has been shown partly in sectionin FIG. 7. This arc chute comprises a pair of spaced sidewalls 85 and 86of electric insulating material such as porcelain. The arc chute isconstructed so that the sidewalls 85 and 86 nest between and extendabove the isolating barriers 82 of the illustrated pole unit. Thesidewalls dene a relatively narrow arcing chamber adjacent the lower endof the chute, as seen in FIG. 7, and a suitable barrier 87 disposedadjacent the lower end of the chute provides a relatively restrictedopening 88 therein.

The restricted opening 88 in chute 83 admits the corresponding free endsof arms 61 and 63 of the movable contact member 14 and the opposing endsof each pair of fingers 30 of the relatively stationary contact member12. Thus all of said ends are enclosed by the spaced sidewalls 85 and 86which are disposed generally parallel to the arcuate paths of movementof the free ends of arms 61 and 63. Accordingly, all of the cooperatingcontact surfaces 32 and 67 are disposed in the narrow arcing chamber.The disposition of the contact surfaces to provide as many as fourparallel points of abutting engagement within a common arcing chamber ofpractical width has been made possible by the particular orientation ofthe movable and relatively stationary contact members 14 and 12described in detail hereinbefore. When the actuating means 15 moves themovable member 14 to effect substantially simultaneous separation ordisengagement of the cooperating contact surfaces during a circuitopening operation of the breaker, an electric arc is initiated withinthe arcing chamber of arc chute 83.

Located intermediate the upper and lower ends of the arc chute 83 are aplurality of spaced-apart metal plates 89 transversely extending betweenthe sidewalls 85 and 86 and disposed generally perpendicular to the pathof the electric arc drawn between the cooperating contact surfaces 32and 67. In a conventional manner, the arc is driven against the exposedlower edges of the plates 89, and these plates chop the arc into afamily of serially related arclets which are subsequently deionized andextinguished as they move within the spaces between adjacent plates.

Such arc-chopping plates 89 contribute to the arc quenching process inseveral different ways. Their relatively cool surfaces reduce thetemperature of the arc thereby enhancing deionization. In order topermanently extinguish the arc and thus interrupt the A.-C. circuitcurrent, it is, of course, necessary to deionize the are gases at acurrent zero thereby preventing the reestablishment or reignition of thearc which is periodically discontinued every half cycle as thealternating current goes through zero. The plates 89 further enhancedeionization by causing a turbulent mixing of the hot arc gases andrelatively cold air in the spaces through which the arclets move, Eacharclet has its own anode and cathode voltage drop region adjacent theopposing surfaces of the associated pair of metal plates where thevoltage gradient is relatively high, and at least a certain minimumpotential difference between the associated plates is required toreestablish the arclet after a current zero. Accordingly, the cumulativeelfect of the plurality of spaced metal plates is to raise thereignition voltage of the circuit interrupter, that is the potentialdifference between the separated contact members 12 and 14 that isrequired to reignite the arc after a current zero, to a point where itexceeds permanently the circuit recovery voltage impressed upon themembers 12 and 14 tending to reestablish the flow of current.

The spaced-apart metal plates 89 are held in place by means ofappropriate vertical grooves 9@ disposed in the opposing surfaces ofsidewalls 85 and S6. As can be seen in FIG. 7, reduced-depth portions ofsome of the grooves 9i) extend below the metal plates S9 in order toincrease the length of the electrical creepage path over this part ofthe surface of the sidewalls. The inner portions of these grooveextensions are shielded from the intense heat of the electric arc in thearcing chamber and hence are cooler than the remainder of the surface ofthe sidewalls. The electric resistance of insulating materials is knownto decrease with increasing temperature, and accordingly the shieldedportions of the surface of the sidewalls provided by the extensions ofgrooves serve to improve the resistance of the surface. Thisconstruction significantly aids the rapid and permanent extinguishmentof the arc drawn between the cooperating contact surfaces 32 and 67 asthey separate.

The arcproducts generated in the arc chute 83 during a circuitinterrupting operation are exhausted or vented through an outlet 9,1provided by an opening between sidewalls 35 and S6 at the upper end ofthe chute. The hot arc products pass upward from the area of the metalplates 89 through spaces provided between insulating barriers or ribs 92which extend across the arc chute above the metal plates. At outlet 91the arc products must pass through a mufer 93 comprising a serpentinestrip of perforated metal. The arc products impinge against the muflier93 and are rapidly cooled thereby. This suppresses ame emisison from thearc chute during a circuit interrupting operation, which flame emissionwould otherwise result if incandescent arc products were exhausted.

The sidewalls 85 and 86 are assembled and held in spaced relation by apair of rivets or bolts 97 extending through transverse members 93 ofthe are chute 83. As is indicated in FIG. 7, the chtite is convenientlymounted on base member 11 by means of an appropriate recess or notch 99provided in transverse member 98. The notch 99 is disposed to receive anupwardly protruding portion of the supporting angle 26, and thesupporting angle 24 is provided with a stud 29 for securing it to theinsulating sheet 20 of the base 11. As has been mentioned hereinbefore,the supporting angle Z4 also serves as an arc runner in cooperation withthe stationary contact member 12.

Turning now to FIGS. 8 and 9, the insulating sheet 20 of the base member11 will be described in detail. In the preferred embodiment of myinvention, the insulating sheet comprises glass liber laminae bondedwith polyester resin. Preferably this material is made ame retardant,i.e., self extinguishing when burned. Manufacture of the insulatingsheet is controlled so that it is substantially uniformly thickthroughout, the thickness being preferably in the order of magnitude of1/s inch. The overall surface area of the illustrated sheet is in theorder of magnitude of well over square inches.

The material mentioned above has the following significantcharacteristics. Minimum physical strength: tensile strength-12,000pounds per square inch; impact strength-l0 foot-pounds per inch of notch(Izod). Minimum dielectric strength: 40() volts per .001 inchperpendicular to laminations; 40,000 volts per inch parallel tolaminations. Dimensional stability: the amount of warp or twist of thematerial varies exponentially as a function of its length, the warp of a36-inch length after 168 hours at 125 degrees centigrade being nogreater than one percent of such length.

The insulating sheet 26 for a 3-pole circuit breaker is molded into theshape indicated in FIGS. l and 8. Referring to FIG. 8, the holes spacedalong the vertical outer edges of the sheet are provided to receivebolts or other suitable fastening means for the purpose of connectingthe sheet to the rigid metal frame 23 and for connecting the operatingmechanism and other parts of the circuit breaker to the sheet 20 andframe 23. Holes 19t) and li are also used in connection with fasteningthe sheet 20 to the frame 23, the holes l being located in the bottomsof depressions which have been formed in the sheet in order to improveits rigidity. By means of holes 102, the overcurrent t`rip devices 18may be mounted on the base member. porting bracket 13 of each pole uniton the base member extend through holes 166' in sheet 20.

The spaced apertures lut in the bottom of channelshaped section 22 ofinsulating sheet 26 admit and partially support the lower breaker studsi9, and the portion of each of these studs emerging from section 22 issecured to the sheet by means of a pair of bolts 105 extending throughholes 106 located without this section. Ap'ertures` 107 are provided atspaced intervals along the bottom of the channel-shaped portionZl ofsheet 20 for partially supporting the upper studs 16. The stud 29 of theupper supporting angle 24 of each upper stud 16 eX- tends through a hole108 in sheet 20, and the bolts 27 for the lower supporting angle 25 ofeach upper stud-16 extend through holes 109 inthe sheet. Thus eachbreaker stud is connected for support to sheet 20 at several points, onepoint of Iconnection being made in a channel-shaped section of thesheet. The reinforcing member 53 of the metalframe 23 is disposed behindthe insulating sheet Z in the area between the holes 103 and 109.Sections Z1 and 22 of the sheet are protruding on Ithis side of the basemember as is shown in FIG. 1.

The apertures 1014 and 1-07 in the insulating sheet 20 are preferablylocated in the bottoms of the two spacedapart channel-shaped depressions21 and 2v2. The channel-shaped depressions, which have been referred tohereinbefore, are provided to improve the structural characteristics ofthe base. The centerlines of these trough-like portions of theinsulating sheet 20 extend in a horizontal direction, and the depressedportions run nearly the entire width of the base member. See FIG. 8.

It will be observed in the sectional view shown in FIG. 9 thatcorresponding breaker studs 16 of adjacent po'le units are disposed ingenerally close proximity in parallel relationship with respect to eachother. Whenever a substantial amount of current is being conducted bythese breaker studs, such as during a severe shortcircuit condition,strong sidewise magnetic forces will interact thereon. While suchcurrent is flowing in the same direction in both of the parallel studs,the magnetic force will act to reduce the spacing therebetween. The samemagnetic force will reverse direction and tend to force the studs apartwhenever the current reverses in only one stud. Lateral movement of eachud is rericted by the vertical Walls of the aperture 107 in thechannel-shaped portion Z1 and also by the fastening means 27 and 29which secure the supporting angles 25 and 24; respectively, totheinsulating sheet 2? adjacent the channel shaped portion. T he sidcwisemagnetic force is exerted uniformly per unit length of stud, and sincethe breaker studs 16 extend behind the base member for a greaterdistance than in front of it, it is evident that opposing bendingmoments are established in the channel-shaped portion Zi at thecenterlines of these studs.

The channel-shaped construction of the insulating sheet Ztl in the areaof the breaker studs enables the relatively thin sheet 2.0 tosuccessfully withstand the abovementioned bending moments. The use of achannelshaped or trough-like configuration greatly increases the momentof inertia and the section modulus of the portion of the insulatingsheet being stressed, thereby signincantly increasing its iiexuralrigidity and decreasing the deformation produced in this portion by thebending moments. Those skilled in the art will understand that thespecifically illustrated configuration of base 1l in FIGS. l, S and 9 isnot the only configuration enabling these desirable results to berealized. I contemplate, for example, that instead of the three breakerstuds 16 (or I9) being supported in the elongated channel-shaped portionor depression 21 (or 22)' of constant depth as shown, an oval orround-shaped depression might be formed of the insulating sheet 2t) withthe portions thereof between studs having reduced depth. The ex- Thebolts 51' for mounting the sup-- pression channel-shaped section as usedherein is inended to include such equivalent configurations wherein across-section taken through a depressed. portion of the base isgenerally channel or U-shaped. i

While I have shown and described a preferred form of my invention by wayof. illustration, many modifications will occur to those skilled in theart. Therefore, I contemplate by the concluding claims to cover all suchmodifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. AnKA electric circuit interrupter contact structure comprising:Y abase member; a relatively stationary contact member mounted on the basemember; a pair of spaced-apart lugs mounted on the base member in spacedrelation to the stationary contact member; a pivot pin supported by thelugs to span the space therebetween; a releasable clamp connected to thepivot pin intermediate the lugs to prevent axial movement of said pin,the clamp comprising a resilient coil encircling the pin and havingtangentially extending opposite ends disposed in a cooperating.releasably self-maintained position wherein the circumference of thecoil is contracted so that the coil is rmly grasping the encircled pin,said opposite ends being movable relativeto each other to a differentcooperating position wherein the coil circumference is expanded and thepin thereby released for purposes of removal from said lugs; a movablecontact arm rotatably mounted on the pivot pin and disposed incooperative relationship with the stationary contact member; andactuating means coupled to the movable contact arm for ymoving said arminto and out of circuit making engagement with the stationary contactmember.

2. An electric circuit interrupter contact structure comprising: a basemember; a relatively stationary contact member mounted on the base; apair of spaced-apart lugs mounted on the base in spaced relation to thestationary contact member; a pivot pin supported by the lugs to span thespa-ce therebetween and projecting outwardly trom each lug; a releasableclamp connected to the pivot pin intermediate the lugs to prevent axialmovement of said pin, the clamp comprising a resilient helical coilencircling the pin in the space between said lugs and havingtangentially extending opposite ends arranged for movement between anormal position and a releasable self-locked position, the coil beingdisposed whenever said coil ends are in said releasable self-lockedposition to firmly grasp the encircled pin; a movable contact memberrotatably mounted on the outward projections of the pivot pin adjacentthe outwardly facing sides of both of said lugs, said movable contactmem-ber being disposed in cooperative relationship with the stationarycontact member; and actuating means coupled to the movable contactmember for moving said member into and out of circuit making engagementwith the stationary contact member.

3. In the Contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the basemember; a bracket mounted on the base member in spaced relation to thestationary contact me1nber;an elongated movable contact arm pivotallyconnected to the bracket for rotation on an axis,

. one end of the arm having at least one contact surfaice disposed formovement into and out of circuit making engagement with at least onecooperative contact surface ot' the stationary contact member, said oneend being axially offset with respect to the pivotal connection betweenarm and bracket so that the center of the circuit making surface area ofsaid one end defines with the center of said pivotal connection astraight line intersecting the axis of rotation at an oblique angle; andactuating means connected to the movable contact arm for moving said armabout said axis, said arm being constructed and arranged so that theline of action of the resultant actuating force applied to the armintersects said straight line.

4. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base; abracket mounted on the base in spaced relation to the stationary contactmember; an elongated movable contact arm pivotally connected to thebracket for rotation on an axis, one end of the arm having at least onecontact surfacedisposed for movement into and out of abutting engagementwith at least one cooperative contact surface of the stationary contactmember, said one end being axially offset with respect to the pivotalconnection between arm and bracket so that the center of the engagingsurface area of said one end defines with the center of said pivotalconnection a straight line intersecting the axis of rotation at anoblique angle; and actuating means connected to the movable contact armfor supplying actuating force to move said arm about said axis, said armbeing constructed and arranged so that the actuating force applied tothe arm produces no net moment with regard to said straight line.

5. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base; abracket mounted on the base in spaced relation tothe stationary contactmember, said bracket including a pivot pin; a movable contact membercomprising a pair of generally parallel, spaced-apart elongated armsconnected to the pivot pin for rotation about its axis, said arms havingcontact surfaces at corresponding ends disposed for movement into andout of abutting engagement with cooperating contact surfaces of thestationary contact member, said pair of arms being spaced closertogether at said corresponding ends than at the pivot pin; and actuatingmeans comprising a shaft disposed in parallel relation to the pivot pinand connected to both of the movable contact arms for jointly movingsaid arms about the axis of said pivot pin, said arms being oppositelyoffset at their respective points of connection to said shaft, wherebysaid arms are substantially torsion-free while engaging the stationarycontact member.

6. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the basemember; an electroconductive bracket mounted on the base member inspaced 'relation to the stationary contact member; an elongated movablecontact arm pivotally connected to the bracket for rotation about anaxis, one end of the arm having at least one contact surface disposedfor movement into and out of abutting engagement with at least onecooperative contact surface of the stationary contact member, said oneend being axially offset with respect to the pivotal connection betweenarm and bracket so that the center of the engaging surface area of saidone end together with the center of said pivot connection lie in acommon plane of reaction which intersects the axis of rotation at anoblique angle, the connection between bracket and arm includingcontiguous slide surfaces disposed generally perpendicular to the axisof rotation to form a current-conducting joint, one of said slidesurfaces being substantially flat and the other having a raised sectiondefining with the flat surface a line contact; and an actuating memberconnected to the movable contact arm for moving said arm about saidaxis, the center of the connection between arm and actuating memberbeing disposed substantially in said plane of reaction.

7. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base and a contact finger pivotally supported bysaid electro-conductive member for movement in an arcuate movablecontact arm pivotally connected to the bracket for rotation on an axis,one end of the arm being arcuately movable in a plane intersecting theplane defined by the arcuate path of the contact finger and having atleast one contact surface disposed in circuit making and breakingrelationship with at least one cooperative contact surface of saidfinger, said one end being axially offset with respect to the pivotalconnection between arm and bracket so that the center of the circuitmaking surface area of said one end defines with the center of saidpivotal connection a straight line which intersects the axis of rotationat an oblique angle, the connection between bracket and arm includingcontiguous slide surfaces disposed generally perpendicular to the axisof rotation to form a current-conducting joint, one of said slidesurfaces being substantially fiat and the other slide surface having araised section; and actuating means connected to the movable contact armfor moving said arm about said axis, said arm being constructed andarranged so that the bearing surface between the actuating means and thearm is intersected by said straight line.

8. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base and a contact finger pivotally supported bysaid electro-conductive member for movement in a first plane; anelectroconductive bracket mounted on the base in spaced relation to thestationary contact; an elongated movable contact arm pivotally connectedto the bracket for rotation on an axis, one end of the arm being axiallyoffset with respect to the pivotal connection, the axially offset endbeing arcuately movable in a second plane intersecting said first planeand having at least one contact surface disposed for abutting engagementwith at least one cooperative contact surface of said finger, theconnection between bracket and arm including contiguous slide surfacesdisposed generally perpendicular to the axis of rotation to form acurrent-conducting joint, one of said slide surfaces being substantiallyflat and the other slide surface having a raised section defining withthe flat surface a line contact; and actuating means connected to themovable contact arm to apply actuating force for rotating said arm onsaid axis, the center of the connection between arm and actuating meansbeing disposed so that the line of action of the resultant actuatingforce for rotating the arm together with the center of the con- `tactengaging area of said axially offset end and the center of the pivotalconnection between arm and bracket define a third plane including theintersection of said rst and second planes.

9. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base and disposed to provide a fulcrum, a contactfinger pivotally supported intermediate its ends on the fulcrum, springmeans associated with one end of the contact finger for establishing abiasing torque in the finger, the spring means being disposed so thatthe moment arm between its line of action and the fulcrum is apredetermined length, the contact finger having at its other end acontact surface movable in an arcuate path spaced from the fulcrum adistance greater than said predetermined length, and stop means disposedto engage said other end to determine the limit of its arcuate movementcaused by the biasing torque; an electroconductive bracket mounted onthe base in spaced relation to the stationary contact; an elongatedmovable contact arm pivotally connected to the bracket for rotation onan axis, one end of the arm being arcuately movable in a plane disposedsubstantially perpendicular to the plane of movement of said other endof the contact finger and having at least one contact surface disposedfor abutting engagement with the contact surface of said finger, saidone end of the arm being axially offset with respect to the pivotalconnection between arm and bracket so that the center of the engagingsurface area of said one end defines with the center of said pivotalconnection a straight line which intersects the axis of rotation at anoblique angle, the connection between bracket and arm includingcontiguous slide surfaces disposed generally perpendicular to the axisof rotation to form a current-conducting joint, one of said slidesurfaces being substantially flat and the other slide surface having araised section defining with the at surface a line contact; andactuating means connected to the movable contact arm for moving said armabout said axis, said arm being constructed and arranged so that theresultant actuating force applied to the arm is directed along a line ofaction intersecting said straight line.

10. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base and a contact finger pivotally supported bysaid electroconductive member for movement in an arcuate path; anelectroconductive bracket mounted on the base in spaced relation to thestationary contact; an elongated movable Contact arm pivotally connectedto the bracket for rotation about an axis, one end of the arm beingarcuately movable in `a plane generally perpendicular to the planedefined by the arcuate path of the contact finger and having atransverse contact surface disposed in circuit making and breakingrelationship with an abutting contact surface of said finger, theconnection between bracket and arm including contiguous slide surfacesdisposed generally perpendicular to the axis of rotation to form acurrent-conducting joint; and actuating means coupled to the movablecontact arm for pivotally moving said arm.

l1. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact comprising an electroconductivemember mounted on the base, at least one elongated contact fingerpivotally supported by the electroconductive member, and spring meansfor biasing the contact ringer and permitting limited deflectionthereof; a bracket mounted on the base in spaced relation to thestationary contact; an elongated movable contact arm pivotally connectedto the bracket, one end of the arm being arcuately movable in a planegenerally perpendicular to the longitudinal centerline of said contactfinger and having a transverse contact surface disposed in circuitmaking and breaking relationship with an abutting Contact surface ofsaid finger; and actuating means coupled to the movable contact arm forpivotally moving said arm.

12. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base andincluding at least two separate contact fingers respectively disposedfor relatively limited pivotal movement in generally parallel planes,said fingers having adjacent contact surfaces, respectively; a bracketmounted on the base in spaced relation to the stationary contact member;an elongated movable contact arm pivotally connected to the bracket, oneend of the arm being arcuately movable between open and closed circuitpositions in a plane intersecting the respective planes of movement ofthe contact iingers and having at least one transverse Contact surfacedisposed in abutting relation to the adjacent contact surfaces of saidfingers for substantially simultaneously engaging and disengaging bothof said adjacent surfaces as said one end is moving respectively intoand out of its closed circuit position; and 4actuating means coupled tothemovable contact arm for pivotally moving said arm.

13. In the contact structure of an electric circuit interrupter: a basemember; a relatively stationary contact member mounted on the base andincluding at least one pair of opposing contact fingers disposed forrelatively limited pivotal movement in a common plane, each finger ofsaid pair having a contact surface; a bracket mounted on the base inspaced relation to the stationary contact member; a movable contactmember comprising a pair of arms pivotally connected to the bracket andhaving corresponding ends respectively disposed for varcuate movement ingenerally parallel planes which intersect said common plane, saidcorresponding ends having transverse contact surfaces disposed inabutting relation to the contact surfaces of said fingers, respectively;and actuating means coupled to the movable contact member for jointlymoving said arms and their contact surfaces into and out of circuitmaking engagement with the respective contact surfaces of said fingers.

14. In the contact structure of an electric circuit interrupter; a basemember; a relatively stationary contact member mounted on the basecomprising adjacent pairs of Contact fingers and spring means forbiasing the iingers and permitting relatively limited movement thereof,the fingers of one of said pairs having opposing ends disposed formovement in separate paths respectively parallel to separate paths ofmovement of opposing ends of the adjacent pair of contact fingers, theopposing ends of each pair of fingers being respectively provided withcontact surfaces; a cooperating movable contact member pivotallysupported on the base comprising a pair of arms having correspondingends disposed for joint arcuate movement between open and closed circuitpositions, each of said corresponding ends being provided with at leaston contact surface disposed in cooperative relationship with the contactsurfaces of two of said contactfinger ends having parallel paths ofmovement for substantially simultaneously engaging and disengaging thecontact surfaces of both of said two ends as the corresponding end ismoved respectively into and out of its closed circuit position, wherebyat least four separate points of circuit-closing engagement are providedbetween the movable and relatively stationary contact members; andactuating means coupled to the movable contact member for jointly movingsaid arms.

l5. In a multipole electric circuit breaker, a base member forsupporting generally parallel current-conducting studs of the lbreakerwhich studs are provided for interconnecting the breaker and an electriccircuit located on the opposite side of the base member from thebreaker, with the studs extending through the base member for thispurpose, said base member comprising a rigid sheet of electricinsulating material of substantially uniform thickness shaped to form atleast one channel-shaped section protruding on the electric circuit sideof the base member, said section having a pair of spaced-apart aperturestherein for admitting, respectively, two corresponding breaker studs ofadjacent breaker poles with portions of said two studs emerging fromsaid section for connection to the breaker, said two studs having strongsidewise magnetic forces interacting thereon Whenever currents ofrelatively high magnitudes are being conducted thereby, and a pluralityof supporting members respectively disposed to secure said emergentportions of the studs to the sheet immediately adjacent to saidchannelshaped section, whereby each of said two studs is supported bythe insulating sheet at points within and without its channel-shapedsection and the sheet can withstand said strong sidewise forces withoutundesirable deformation.

16. In a multipole electric circuit breaker connected between source andload circuits, a base member for supporting in parallel spaced relationtwo pairs of current-conducting breaker studs connected to the sourceand load circuits, respectively, said base member comprising a singlesheet of rigid electric insulating material of substantially uniformthickness molded to form at least two spaced-apart channel-shapedsections protruding on the opposite side of the base member from thebreaker, portions of both source studs being disposed within a first oneof said channel-shaped' sections and being connected thereto forsupport, portions of both load studs being disposed within a second oneof said channel-shaped sections and being connected thereto for support,and a plurality or" supporting members connect-v i9 ing the respectivestuds to the breaker side of the base member adjacent to achannel-shaped section thereof for additionally supporting the studswithout said channelshaped sections, whereby said insulating sheet isable to withstand strong magnetic forces acting on the studs whenrelatively high currents are flowing therein.

17. In an electric circuit breaker, a base member supporting all of thecurrent-conducting studs and other breaker parts directly connected tothe studs, said base member comprising a metal frame and at least onerigid sheet of electric insulating material of substantially uniformthickness attached to said frame, the sheet being molded to form achannel-shaped depression for partially supporting at spaced intervalsalong the bottom of the depression at least two of thecurrent-conducting studs, said two studs respectively having portionsthereof emergning from the depression which portions are subject tostrong lateral magnetic forces when currents of relatively highmagnitudes are being conducted thereby, and

.separate means for further supporting each of said two studs fromnon-depressed portions of the sheet, each of said means comprising asupporting member disposed rigidly to secure the emergent portion of astud to a portion of the sheet adjacent to the lip of the depressiontherein, whereby said strong lateral forces are withstood by the sheetwithout undesirable deformation thereof.

18. In an electric circuit breaker: a base member comprising a sheet ofsubstantially uniformly thick electric insulating material formed todene two spaced-apart trough-like portions; at least one pair ofcurrent-conducting studs respectively connected for partial support tothe trough-like portions of said sheet; a relatively stationary contactmember connected to one stud of said pair; support means secured to thesheet for supporting said stationary contact member and having anintegral part disposed adjacent one surface of the sheet intermediatethe trough-like portions; a bracket mounted on the sheet and having anintegral part disposed adjacent said one surface of the sheetintermediate the trough-like portions in spaced relation to said supportmeans; a movable contact arm pivotally supported by the bracket andconnected to the other stud of said pair, said arm being disposed formovement into abutting engagement with the relatively stationary contactmember; actuating means coupled to the movable contact arm for pivotallymoving said arm; and a rigid reinforcing member disposed adjacent theopposite surface of the sheet intermediate the trough-like portions inoverlapping relationship with the integral parts of said support meansand bracket.

19. An electric circuit interrupter: a base member comprising a singlesheet of substantially uniformly thick electric insulating materialformed to define two spacedapart trough-like portions having aperturesin the bottoms thereof; a pair of current-conducting studs extendingfrom the rear to the front of the sheet, each of said studs beingdisposed in an aperture of a different troughlike portion; a relativelystationary contact connected to one of said studs; support means securedto the sheet for supporting said stationary contact and having anintegral part disposed adjacent the front surface of the sheetintermediate the trough-like portions; a bracket mounted on the sheetand having an integral part disposed adjacent the front surface of thesheet intermediate the trough-like portions in spaced relation to saidsupport means; a movable contact arm pivotally supported by the bracketand connected to the other stud of said pair, said arm being disposedfor rearward movement into abutting engagement with the stationarycontact; actuating means coupled to the movable contact arm forpivotally moving said arm; and a rigid frame for supporting the sheetadjacent its outer edges and including at least one reinforcing memberdisposed adjacent the rear surface of the sheet intermediate thetrough-like portions 2t) in overlapping relationship with the integralparts of said support means and bracket.

20. In an electric circuit breaker: a base member for supporting a pairof current-conducting studs of the breaker, said base member comprisinga unitary sheet of electric insulating material of substantially uniformthickness molded to form a pair of spaced-apart channelshaped sections,the breaker studs being connected for support to the sheet at aplurality of points, at least one point of connection of each stud beingmade in a different one of said channel-shaped sections; a contactfinger supported by one of the current-conducting studs for pivotalmovement in a first plane; spring means for biasing the contact fingerand permitting limited deflection thereof; a bracket mounted on thesheet in spaced relation to the contact finger; an elongated movablecontact arm pivotally connected to the bracket and electricallyconnected to the other current-conducting stud, one end of the arm beingarcuately movable in a plane intersecting `said first plane and having atransverse contact surface disposed in circuit making and breakingrelationship with an abutting contact surface of said finger; andactuating means coupled to the movable contact arm for pivotally movingsaid arm.

21. In an electric circuit breaker: a metal frame; a base membercomprising a unitary sheet of not more than 1t-inch thick electricinsulating material mounted adjacent its outer edges on the metal frame,the sheet being disposed to form a pair of channel-shaped portions thebottoms of which have apertures for admitting and restricting lateralmovement of the current-conducting studs of the breaker; a contactfinger pivotally supported by one of the current-conducting studs formovement in an arcuate path; a bracket mounted on the sheet in spacedrelation to the contact finger; an elongated movable contact armpivotally connected to the bracket, one end of the arm having atransverse contact surface disposed for arcuate movement in a planeintersecting the plane defined by the arcuate path of the contactfinger; and actuating means coupled to the movable contact arm formoving said transverse contact surface into and out of circuit makingengagement with an abutting contact surface of -said contact finger.

22. In an electric circuit breaker: a base member supporting thecurrent-conducting studs and other breaker parts directly connected tothe studs, said base member comprising a single sheet of electricinsulating material of substantially uniform thickness shaped to form atleast one channel-shaped depression having at least one aperture in itsbottom for admitting one of the currentconducting studs; a contactfinger pivotally connected to said one stud for movement in an arcuatepath; an electroconductive bracket mounted on the sheet in spacedrelation to the contact finger and connected to anothercurrent-conducting stud; an elongated movable Contact arm pivotallyconnected to the bracket for rotation on an axis, one end of the armbeing arcuately movable in a plane generally perpendicular to the planedefined by the arcuate path of the contact finger and having atransverse contact surface disposed in circuit making and breakingrelationship with an abutting contact surface of said finger, theconnection between bracket and arm including contiguous slide surfacesdisposed generally perpendicular to the axis of rotation to form acurrentconducting joint; and actuating means coupled to the movablecontact arm for pivotally moving said arm.

23. In an electric circuit interrupter: a base member comprising a sheetof substantially uniformly thick electric insulating material, twospaced-apart trough-like depressions being formed of the sheet; at leastone pair of current-conducting studs respectively connected for partialsupport to the trough-like depressions of said sheet; support meanssecured to the sheet for partially supporting one of the studs andhaving an integral part disposed adjacent a front surface of the sheetintermediate the trough-like depressions; at least one contact lingerconnected to said one stud for relatively limited pivotal movement in afirst plane; a bracket mounted on the sheet and having an integral partdisposed adjacent the front surface of the sheet intermediate thetrough-like depressions in spaced relation to said support means; amovable contact arm connected to the other stud of said pair andsupported by the bracket for pivotal movement in a plane intersectingsaid rst plane, one end of said arm having a transverse contact surfacedisposed for rearward movement in circuit making relationship with anabutting contact surface of said finger; actuating means coupled to themovable contact arm for pivotally moving said arm; and a rigidreinforcing member disposed adjacent a rear surface of the sheetintermediate the trough-like depressions in overlapping relationshipwith the integral parts of said support means and bracket.

24. In an electric circuit interrupter: a base member comprising a rigidframe and a single sheet of substantially uniformly thick electricinsulating material mounted on the frame, said sheet being formed toinclude a pair of spaced-apart trough-like portions having openings intheir bottoms; a pair of current-conducting studs extending from therear to the front of the sheet, each of said studs being disposed in anopening of a different troughlike portion; a relatively stationarycontact member connected to one of said studs for pivotal movement in afirst plane; support means secured to the sheet for supporting saidstationary contact and having an integral part disposed adjacent thefront surface of the sheet intermediate the trough-like portions; anelectroconductive bracket mounted on the sheet and having an integralpart disposed adjacent the front surface of the sheet intermediate thetrough-like portions in spaced relation to said support means; at leastone reinforcing member aflixed to said rigid frame and disposed adjacentthe rear surface of the sheet intermediate the trough-like portions inoverlapping relationship With the integral parts of said support meansand bracket; an elongated movable contact arm pivotally supported by thebracket and connected to the other stud of said pair, said arm beingdisposed for rotation on an axis oriented generally parallel to thelongitudinal centerlines of the trough-like portions of the sheet, oneend of the arm being arcuately movable in a second plane intersected bysaid irst plane and having at least one contact surface disposed forabutting engagement with at least one cooperative contact surface ofsaid relatively stationary contact member, said one end being axiallyoffset with respect to the pivotal connection between arm and bracket,the bracket and arm respectively including contiguous slide surfacesdisposed generally perpendicular to the axis of rotation to form acurrentconducting joint; and actuating means connected to the movablecontact arm to apply actuating force for rotating said arm on said axis,the center of the connection between arm and actuating means beingdisposed so that the line of action of the resultant actuating force forrotating the arm together with the center of the contact engaging areaof said one end and the center of the pivotal connection between arm andbracket define a third plane including the intersection of said firstand second planes.

25. In the contact structure of an electric circuit intenrupter: a basemember; a relatively stationary contact member mounted on the basemember; an electroconductive bracket mounted on the base member inspaced relation to the stationary contact member and including aIremovable pivot pin; a movable contact arm rotatably mounted on saidpivot pin for arcuate movement at one end into and out of circuit makingengagement with the stationary contact member, the arm and the brackethaving contiguous slide surfaces disposed generally perpendicular to theaxis of the pivot pin to form a currentconducting joint, one of saidsurfaces being substantially ilat and the other surface having a raisedsection delining with the dat surface a line Contact; spring means formaintaining contact pressure between the contiguous surfaces for .ingthe joint as the movable contact arm rotates; a relea'sable clampconnected to the pivot piny to prevent axial movement or" said pin, theclamp comprising a resilient coil encircling and firmly grasping the pinto prevent removal thereof from the bracket, the opposite ends of thecoil being arranged for cooperative movement to expand the coilcircumference and thereby release the pivot pin to permit removalthereof; and actuating means coupled to the movable contact arm forrotating said arm on the pivot pin.

26. ln an electric circuit interrupter: a base member; a relativelystationary contact member mounted on the base and including a pair ofopposing contact fingers disposed i`or relatively limited pivotalmovement in a common plane, the opposing ends of said fingers havingcomplementary contact surfaces, respectively; a bracket mounted on thebase in spaced relation to the stationary contact member; a movablecontact member comprising a pair of arms pivotally connected to thebracket and having corresponding ends respectively disposed for arcuatemovement in generally parallel planes which intersect said common plane,said corresponding ends having transverse contact surfaces disposed inabutting relation to the complementary contact surfaces of saidiingers,'1e spectively; actuating means coupled to the movable contactmember for jointly moving the contact surfaces of both of said arms intoand out of circuit making engagement with the respective complementarycontact surfaces; `and an arc chute mounted on the base comprising apair of spaced sidewalls dening an arcing chamber adiacent one end ofthe chute, an outlet at another end of the chute and a plurality ofspaced-apart, arc-chopping metal plates disposed substantiallyperpendicular to the sidewalls at a location intermediate the outlet andsaid one end of the chute, said arc chute having at its one end arelatively restricted opening for admitting the opposing ends of saidfingers and the corresponding ends of said arms, whereby all of saidcontact surfaces are disposed in the arcing chamber.

27. In an electric circuit interrluptetr: a base member; a relativelystationary contact member mounted on the base comprising two adjacentpairs of opposing contact elements, the opposing ends of the elements ofeach pair being respectively provided with complementary contactsurfaces disposed in a common plane; a bracket mounted on the base inspaced relation to the stationary contact member; a movable contactmember pivotally connected to the bracket comprising a pair of armshaving corresponding ends respectively disposed for joint arcuatemovement between open and closed circuit positions in generally parallelplanes intersecting said common plane, each of the corresponding ends ofsaid arms being provided with at least one contact surface disposed incooperative relationship with the contact surfaces oftwo differentcontact elements for substantially simultaneously engaging the contactsurfaces of both of said two elements during a circuit closing operationof the circuit interrupter, whereby at least four separate points ofcircuit-closing engagement are provided between the movable andrelatively stationary contact members; an arc chute mounted on the basecomprising a pair of spaced sidewalls disposed generally parallel to therespective planes of movement of the corresponding ends of said arms andenclosing said corresponding ends and the opposing ends of both pairs ofcontact elements thereby to enclose and extinguish the electric arcdrawn upon disengagement of the cooperating contact surfaces during acircuit opening operation of the circuit interrupter, said arc chuteincluding an outlet for exhausting the arc products and a pluralityof-spaced-apart metal plates transversely extending between thesidewalls at a location intermediate said outlet and said cooperatingcontact surfaces, said metal plates being disposed generallyperpendicular to 23 the path of the electric arc for chopping said arcinto a family of serially related arclets; and actuating means coupledto the movable contact member for jointly moving said arms to obtaincircuit opening and closing operations.

28. In an electric circuit interruptor: a base member; an arc chutemounted on the base comprising a pair Of spaced sidewalls defining anarcing chamber adjacent one end of the chute, an outlet at another partof the chute, and a plurality of spaced-apart, arc-chopping metal platesdisposed substantially perpendicular to the sidewalls at a locationintermediate the arcing chamber and outlet of the chute; means forinitiating an electric arc within said arcing chamber comprising movableand relatively stationary contact members supported on the base andextending into the arc chute at said one end, the Contact members beingprovided with cooperating contact surfaces respectively disposed in saidarcing chamber for relative movement into and out of circuit making engagement, at least one of the contact members having at least twoseparate contact surfaces for establishing parallel points of engagementbetween the cooperating contact surfaces; and actuating means coupled tothe movable contact member for moving said member to effectsubstantially simultaneous disengagement of all of said cooperatingcontact surfaces.

29. In an electric circuit breaker: a base member; a relativelystationary contact comprising an electroconductive member mounted on thebase, at least one elongated contact finger pivotally supported by theelectroconductive member, and spring means for biasing the contactfinger and permitting limited defiection thereof; a bracket mounted onthe base in spaced relation to the stationary contact; an elongatedmovable contact arm pivotally connected to the bracket, one end of thearm being movable in an arcuate path defining a plane generallyperpendicular to the longitudinal centerline of said contact linger andhaving a Contact surface disposed in circuit making and breakingrelationship with a cooperating contact surface of said finger; an' arcchute mounted on the base comprising a pair of sidewalls disposedgenerally parallel to and on opposite sides of the arcuate path ofmovement of said one end for enclosing the electric arc drawn betweensaid cooperating contact surfaces during a circuit breaking operationthereof, said arc chute including an opening for exhausting the arcproducts and a plurality of spaced-apart metal plates transverselyextending between the sidewalls at a location intermediate said openingand said cooperating contact surfaces, said metal plates being disposedgenerally perpendicular to the electric arc for chopping the arc into afamily of serially related arclets; and actuating means coupled to themovable contact arm for moving said arm to obtain circuit making andbreaking operations of said cooperating contact surfaces.

30. In an electric circuit breaker: a base member; a relativelystationary contact member mounted on the base comprising a pivotallysupported contact finger disposed for relatively limited deflection in afirst plane; an elongated movable contact member pivotally supported onthe base for movement in a second plane perpendicular to the rst plane,said movable contact member having a contact surface disposed formovement along an arcuate path into and out of circuit making engagementwith a cooperating contact surface of said finger; an arc chute mountedon the base comprising a pair of sidewalls disposed generally parallelto said second plane on opposite sides of said arcuate path forenclosing the electric are initiated upon disengagement of thecooperating contact surfaces, said arc chute including an outlet forexhausting the arc products and a plurality of spaced-apart arc-choppingmetal plates disposed between the sidewalls intermediate said outlet andthe area of arc initiation, the opposing surfaces of said sidewallsbeing respectively provided with a plurality of grooves for receivingsaid metal plates and said grooves being extended beyond the metalplates along portions of the sidewalls adjacent the area of arcinitiation; and actuating means coupled to the movable contact memberfor pivotally moving said member and thereby effecting engagement anddisengagement of the cooperating contact surfaces.

3l. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact member mounted on the basecomprising a pivotally supported contact finger disposed for relativelylimited deflection in a first plane; an electroconductive supportingbracket mounted on the base in spaced relation to the stationary contactmember; an elongated movable contact member pivotally connected to thebracket for movement in a second plane perpendicular to the first plane,the connection between supporting bracket and movable contact memberincluding contiguous slide surfaces disposed generally parallel to thesecond plane to form a current-conducting joint, one of said surfacesbeing substantially fiat and the other being raised so that thecontiguous portions of the surfaces define a straight line oriented atapproximately a right angle with respect to the longtudinal centerlineof the movable contact member; abutting contact surfacesY respectivelydisposed on said contact finger and said movable contact member incircuit making and breaking relationship; and actuating means coupled tothe movable contact member to move said member.

32. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact member mounted on the basecomprising a yieldably supported element having a generally fiat contactsurface; a bracket mounted on the base in spaced relation to thestationary contact member; an elongated movable contact arm supportednear one end by the bracket and having at its other end a transversecontact surface disposed for movement in a direction generallyperpendicular to said flat contact surface into circuitmaking abuttingengagement therewith, said transverse surface being curved to definewith the abutting surface of said element a straight-line contactoriented generally parallel to the longitudinal centerline of the arm,the

cooperating Contact surfaces being constructed and arranged so that thecurved transverse surface extends beyond the fiat surface at oppositeends of said straight-line contact; and actuating means coupled to themovable contact arm for moving said arm.

33. In the contact structure of an electric circuit breaker: a basemember; a relatively stationary contact member mounted on the basecomprising a yieldably supported element having a first contact surface;a bracket mounted on the base in spaced relation to the stationarycontact member; a movable contact arm pivotally connected to the bracketand having an elongated contact surface disposed for movement into andout of circuitmaking abutting engagement with the first contact surface,the elongated surface being movable along an arcuate path whichintersects the first surface substantially perpendicular thereto and theelongated surface being oriented with its lengthwise dimension in theplane of said arcuate path of'movement; one of said surfaces beingcurved relative to the other to establish between the surfaces when inabutting engagement a straight-line contact the length of which isshorter than the length of said elongated surface; and actuating meanscoupled to the tmovable contact member for pivotally moving saidlmember.

References Cited in the file of this patent UNITED STATES PATENTS (Otherreferences on following page) UNITED STATES PATENTS Massey Nov. 14, 1933Sandin Sept. 20, 1938 Sachs Aug. 6, 1940 Scott May 8, 1945 5 Caswell May3l, 1949 Kojis Sept. 11, 1951 Dickinson et al Oct. 28, 1952 Strom et al.Aug. 11, 1953 Cole Mar. 23, 1954 10 Beatty Oct. 5, 1954 Hulteen et al.Jan. 24, 1956 Despard Jan. 29, 1957 Ramrath Mar. 5, 1957 Cassidy Mar.12, 1957 15 Page et al. Aug. 13, 1957 26 Bires et al Ian. 28, 1958 Mikoset al, Jan. 28, 1958 Souchet May 27, 1958 Mathews Dec. 16, 1958 AllenFeb. 24, 1959 Favre July 14, 1959 Naimer Sept. 8, 1959 Caswell Sept. 22,1959 Filliette Mar. 22, 1960 Bonnefois et al. Apr. 26, 1960 BaskervilleMar. 24, 1960 Baskerville et al Mar. 31, 1960 Scully Nov. 29, 1960FOREIGN PATENTS Germany Oct. 9, 1934 Great Britain June 12, 1957

1. AN ELECTRIC CIRCUIT INTERRUPTER CONTACT STRUCTURE COMPRISING: A BASEMEMBER; A RELATIVELY STATIONARY CONTACT MEMBER MOUNTED ON THE BASEMEMBER; A PAIR OF SPACED-APART LUGS MOUNTED ON THE BASE MEMBER IN SPACEDRELATION TO THE STATIONARY CONTACT MEMBER; A PIVOT PIN SUPPORTED BY THELUGS TO SPAN THE SPACE THEREBETWEEN; A RELEASABLE CLAMP CONNECTED TO THEPIVOT PIN INTERMEDIATE THE LUGS TO PREVENT AXIAL MOVEMENT OF SAID PIN,THE CLAMP COMPRISING A RESILIENT COIL ENCIRCLING THE PIN AND HAVINGTANGENTIALLY EXTENDING OPPOSITE ENDS DISPOSED IN A COOPERATINGRELEASABLY SELF-MAINTAINED POSITION WHEREIN THE CIRCUMFERENCE OF THECOIL IS CONTRACTED SO THAT THE COIL IS FIRMLY GRASPING THE ENCIRCLEDPIN, SAID OPPOSITE ENDS BEING MOVABLE RELATIVE TO EACH OTHER TO ADIFFERENT COOPERATING POSITION WHEREIN THE COIL CIRCUMFERENCE ISEXPANDED AND THE PIN THEREBY RELEASED FOR PURPOSES OF REMOVAL FROM SAIDLUGS; A MOVABLE CONTACT ARM ROTATABLY MOUNTED ON THE PIVOT PIN ANDDISPOSED IN COOPERATIVE RELATIONSHIP WITH THE STATIONARY CONTACT MEMBER;AND ACTUATING MEANS COUPLED TO THE MOVABLE CONTACT ARM FOR MOVING SAIDARM INTO AND OUT OF CIRCUIT MAKING ENGAGEMENT WITH THE STATIONARYCONTACT MEMBER.